AuthorTopic: MP-1 Classic Information (Read 2135 times)

Hi guys, I've owned an MP-1 Classic since around 1997 and I've noticed that there seems to be little information on it compared with the MP-1. Soooo, I'm hoping I can provide a little remedy for that issue. After needing to replace a few parts and wondering about mods, I decided to take a serious look at the schematics. Luckily, I had a set which I downloaded long ago from the old adadepot site (copies of which may be found on: http://www.lydian.ca/ADA_MP-1.html. - not me, by the way).

However, the schematics are very difficult to read, mainly because there are two different preamps contained on the same schematics, sharing some parts, some with different values and not sharing others. I am redrawing all of these and will post them eventually if anyone is interested. My goal is to make sure these are drawn to make the function of everything as clear as humanly possible, along with notes from calculations/measurements I've done personally. (The other preamp on the schematic is apparently called an MP-1 Plus. Was this ever made? Has anyone ever seen one?)

Here are a few things about the Classic:

If anyone has or plans to buy one and wants to clearly see the difference in how overdrive 1 and overdrive 2 works, I suggest the following exercise. Turn OD 2 all the way down and OD 1 all the way up. Strum a chord. Play something. Reverse the settings of OD 1 and OD 2. Repeat what you played before. The difference will be very obvious, or should be. Create a separate patch for each if that helps. That goes a lot further than the info I've seen for trying to get various tones from the original MP-1, which probably would apply to it as well.

Mods:Changing op amps is probably pointless. The Classic is very well designed and although none of the opamps are gold plated parts, good circuit design dictates that circuits should be as independent as possible from specific components after some minimum level. The Classic mostly uses TL072 and 5532 opamps. The TL072s are mostly used for DC, so replacing them with something "better" probably won't hurt as long as you use fet op amps, but if it helps, the original was probably defective. The 5532s are the opamps which are mostly in the signal path and the same applies here, except these should be bipolar input opamps. I know it's tempting to change parts to "make something work better," but David Tarnowski apparently knows how to design this stuff better than most. There are a few other opamps used, but these matter even less apart from meeting what they need to do, like supply more current than a TL072.

If you are trying to get your preamp to sound like a jmp-1, buy a jmp-1. That being said, there appears to be interesting possibilities to change the sound of a Classic to provide more resemblance to a Marshall without changing the Classic's sound too much where you want the Classic to sound like what it is, although I haven't had time to investigate this yet. In particular, the obvious thing is to hand a diode bridge off of one of the tube grids (although probably not the first tube, V1A). There are five "control lines," F1-F5 and at least one of those, F3, is not used. Whether it can be exploited in some way depends on what's programmed into the rom, since it may be the same rom used for the MP-1 Plus that's on the same schematic and does use that line.

Most of the FETs are used as switches so if any need to be replaced, you don't need to find the original 2sk164, if you can't find one. (All the FETs are 2sk164.). The exception is the input stage. It definitely needs to be a low noise FET with similar characteristics. I haven't looked to see what will work, but when I do, I'll post the info.

I've analyzed a few sections of the circuitry and if anyone is interested, I'll post some info about how some of the features work and what changing various components will do. I've done some spice simulations of a few things, like the cabinet simulator and input stage and I plan to get around to the eq section eventually. With a couple of exceptions all of the filters in the eq and cabinet simulator are sallen-key types and changing the frequency bands requires only changing a couple of resistors and capacitors for each band.

Hey Nomes-Electronic, thanks for all the input and insight, and yes please share/post, very interested In Australia, the MP1 was imported (I knew the importer so got an early one), and then MP2, we (well I at least) didn't get to see the variations in between like MP1+, MP1 Classic. So when the MP2 came out, I sold my MP1 rig to a mate so I could buy MP2, love it, I like MP1 but prefer for lots of reason MP2.There's a section for MP1 Classic (Dantes also a fan IIRC). Please add as you can Cheers Richard